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Synopsis: Warming the surgical site or the patient for 30 minutes before clean surgery reduces the incidence of wound infections by half.
Source: Melling AC, et al. Effects of preoperative warming on the incidence of wound infection after clean surgery: A randomized controlled trial. Lancet 2001; 358:876-880.
Abstract: Melling and colleagues at the University Hospital of North Tees in the United Kingdom undertook a study of 421 patients scheduled for either a breast biopsy, hernia repair, or varicose vein surgery to determine the effect of warming on the incidence of wound infection.
Patients were randomized to receive at least a half hour of body warming with a forced air warming blanket (which produced a rise in body temperature by 0.35°C), or a local noncontact radiant heat dressing (which raised the body temperature by 0.13°C), or standard care.
A postoperative infection was diagnosed if there was purulent drainage for five days or painful erythema plus antibiotic therapy within six weeks after surgery. An investigator interviewed and examined patients at two and six weeks after the operation. They found the infection rates to be 5% for those who were warmed and 14% for those who were not, with a P value of less than 0.001. The local and systemic warming effects were almost identical. Wound scores by the ASEPSIS system also were lower for the warmed groups. There were no differences in the incidence of hematomas or seromas. The use of antibiotics also was lower in the warmed group at the P level of 0.002.
Commentary by Alan D. Tice, MD, FACP, of Infections Limited, Tacoma, WA.
The work by Melling, et al is basic but logical. Warming an area of surgery increases the tissue oxygen partial pressure — an effect that can last for up to three hours. This was noted as early as 1956 but no one seems to have picked up on it or applied this knowledge since then. The circulation to the operative wound clearly is increased also by the heat. There were no apparent adverse effects associated with either of the heating techniques. This is in contrast to other interventions, such as prophylactic antibiotics.
Melling, et al make the point that warming an anticipated area of surgery preoperatively may be as effective as giving prophylactic antibiotics with clean surgery. This is an excellent point and may be practical as well. It is certainly less expensive, associated with fewer adverse effects, and less harmful to our fragile microbiology environment with the increasing problem of multidrug-resistant bacteria. It also avoids the problem of which antibiotic to use and how to use it.
It is interesting to note that there have been attempts to cool wounds as well with clean surgery — especially with orthopedics. The cooling may reduce swelling and inflammation but might reasonably be associated with an increase in wound infections — as has been demonstrated with animals more than a decade ago.
The idea of warming up a patient or an area of the body preoperatively is another example of applying some common sense and basic insight that somehow seems to have been overlooked in the quest for more medicines or high-tech solutions for problems. There also has been insight into the benefits of simply giving oxygen to patients during surgery,1,2 and of leaving barrier dressings in place to protect the wound from the introduction of bacteria.3
A confirmatory study is in order but, if the results are correct, there are a lot of other questions to answer. How long should the body be kept warm? Do the benefits increase with warming during or after surgery? How much heat is best? Are the attorney-approved heating pads in the hospitals adequate and effective? Are there added or synergistic benefits to warming with nasal oxygen?
1. Greif R, et al. Supplemental perioperative oxygen to reduce the incidence of surgical wound infection. N Engl J Med 2000; 342:161-167.
2. Muder R. Reducing surgical wound infections with supplemental oxygen. Infectious Disease Alert 2000; 19:89-90.
3. Rubio PA. Use of semiocclusive, transparent film dressings for surgical wound protection: Experience in 3637 cases. Int Surg 1991;7 6:253-254.